One of the receptacle terminals on the TT 7 pin plug is supposed to power the running lights.
One of the receptacles on the TT 7 pin plug is supposed to come from the battery.
According to the latest issue of Trailer Life magazine, if you jump the 12 volt receptacle terminal to the running light receptacle terminal with a fused jumper wire, the lights should light. If the circuit is open they will not light. If the circuit is shorted it will blow the jumper wire fuse.
A fused wire jumper can be purchase at the auto parts store.
If this is too complicated, sometime it is easier, though more expensive, to let the pros do it.